<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>02_外间距测试</title>
    <style>
        body{
            margin: 0;
        }
        *{
            margin: 0;
            padding: 0;
        }
        .fu{
            background-color: rgba(255,255,0,.3);
            /*父子粘连/贴边:
            现象：首个子元素的上外间距与最后一个子元素的下外间距会超出父元素的范围
            解决：给父元素形成BFC结界保护*/
            overflow: hidden;
        }
        .fu>div {
            width: 100px;
            height: 100px;
            background-color: rgba(0,0,255,.6);
            border: 2px solid #00f;
            color: #fff;
            font-size: 25px;
            font-weight: bold;
        }
        .z1 {
            margin-top: 50px;
            margin-bottom: 50px;

        }
        .z2{
            margin-top: 100px;
        }
        .z3{
            margin: 10px;
            margin: 5px 10px;
            margin: 5px 10px 3px 2px;
            margin: 0 auto;
        }
        .z4{
            margin-bottom: 50px;
        }
        .s2{
            /*行内元素垂直方向上的外间距不生效*/
            margin: 5px;
        }

    </style>
</head>
<body>
    <span>span</span><span class="s2">span2</span><span>span3</span>
    <div class="fu">
        <div class="z1">子元素1</div>
        <div class="z2">子元素2</div>
        <div class="z3">子元素3</div>
        <div class="z4">子元素4</div>
    </div>
</body>
</html>